Image sensing circuit and method capable of obtaining higher image brightness dynamic range

ABSTRACT

An image sensing circuit includes floating node, switch circuit, capacitor(s), and counting circuit. The floating node receives image electric charge from a photosensitive pixel. The switch circuit is coupled between floating node and capacitor(s) to dynamically connect and disconnect floating node and capacitor(s). The capacitor(s) include(s) first terminal(s) connected to switch circuit and second terminal(s) connected to ground. The counting circuit counts the number of charging and discharging behavior of capacitor(s) according to dynamic switches of switch circuit wherein the switch circuit dynamically switches to make capacitor(s) be charged and discharged dynamically in response to one exposure time period to receive energy of image electric charge which is determined by the number of charging and discharging behavior of the capacitor(s) and the capacitor(s)&#39; potential value measured finally.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensing mechanism, and moreparticularly, to an image sensing circuit and method.

2. Description of the Prior Art

Generally speaking, image sensing circuits employed in the existingphotosensitive elements usually achieve an effect with a high imagebrightness dynamic range by performing superposition of multiple imagesor increasing the sizes of physical capacitors within the photosensitiveelements; however, the former needs multiple images to be shot, and thelatter increases circuit cost due to the fact that a larger capacitorwill occupy a larger circuit area. Hence, both of them have their owndrawbacks.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide an image sensingcircuit and method capable of obtaining a highest image brightnessdynamic range in a single image with a lower circuit cost, to solve theproblems of the existing arts.

According to an embodiment of the present invention, an image sensingcircuit is disclosed. The image sensing circuit includes a floatingnode, a switch circuit, at least one capacitor, and a counting circuit.The floating node is arranged to receive image electric charge from aphotosensitive pixel. The switch circuit is coupled between the floatingnode and the at least one capacitor, and is arranged to dynamicallyconnect and disconnect the floating node and the at least one capacitor.The at least one capacitor includes a first terminal coupled to theswitch circuit and a second terminal coupled to a ground level. Thecounting circuit is coupled to the switch circuit, and is arranged tocount a number of times of charging and discharging the at least onecapacitor according to dynamic switching of the switch circuit, whereinthe switch circuit dynamically switches to make the at least onecapacitor be dynamically charged and discharged in response to oneexposure time period to receive energy of the image electric charge, andthe energy of the image electric charge is determined by the number oftimes of charging and discharging behavior counted by the countingcircuit and a finally measured potential value of the at least onecapacitor.

According to another embodiment of the present invention, a methodarranged for an image sensing circuit is further disclosed. The methodincludes: providing a floating node arranged to receive image electriccharge from a photosensitive pixel; utilizing a switch circuit coupledbetween the floating node and at least one capacitor, wherein the atleast one capacitor includes a first terminal coupled to the switchcircuit and a second terminal coupled to a ground level; dynamicallyconnecting and disconnecting the floating node and the at least onecapacitor to make the at least one capacitor be dynamically charged anddischarged in response to one exposure time period to receive energy ofthe image electric charge; and counting a number of times of chargingand discharging the at least one capacitor; wherein the energy of theimage electric charge is determined by the counted number of times ofcharging and discharging of the at least one capacitor and a finallymeasured potential value of the at least one capacitor.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating an image sensing method/mechanismaccording to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an image sensing circuit according tothe first embodiment of the present invention.

FIG. 3 is a diagram illustrating an image sensing circuit according tothe second embodiment of the present invention.

FIG. 4 is a diagram illustrating an image sensing circuit according to athird embodiment of the present invention.

FIG. 5 is a diagram illustrating the signal waveforms of the signals Qand QB shown in FIG. 4.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a flowchart illustrating an imagesensing method/mechanism according to an embodiment of the presentinvention. The image sensing method/mechanism of the present inventioncan estimate energy of image electric charge of a photosensitive pixelvia the dynamic charging and discharging behavior of at least onecapacitor, wherein the photosensitive pixel means a pixel unit of aphotosensitive element, and the pixel unit may generate differentamounts of energy of image electric charge under conditions of differentlight source environments (different exposure environments). The imagesensing method of the present invention can precisely estimate an amountof energy of image electric charge (which is generated by aphotosensitive pixel) via the charging and discharging behavior of asingle capacitor or multiple capacitors (i.e., two or more than twocapacitors), so as to correctly calculate a dynamic range of imagebrightness. The image sensing method of the present invention issuitable for different exposure environments, and more particularly, foran exposure environment with strong light to avoid overexposure. Byusing the image sensing method of the present invention, it is capableof obtaining a highest image brightness dynamic range within apredetermined shutter time allowed for shooting a single image withoutincreasing the circuit cost greatly. Compared with the existing arts,the method of the present invention can obtain the highest imagebrightness dynamic range even though the capacitance of a capacitor (ormultiple capacitors) employed by the present invention is smaller (ormuch smaller) than the capacitance of a capacitor employed by theexisting arts. In addition, the above-mentioned mechanism is alsosuitable for the roller blind/rolling shutter and the global shutter.Provided that substantially the same result is achieved, the steps ofthe flowchart shown in FIG. 1 need not be in the exact order shown andneed not be contiguous; that is, other steps can be intermediate. Theflow of the image sensing method of the present invention is detailed asfollows.

Step 105: Provide a floating node to receive image electric charge froma photosensitive pixel;

Step 110: Utilize a switch circuit which is coupled between the floatingnode and at least one capacitor, wherein the at least one capacitor hasa first terminal coupled to the switch circuit and a second terminalcoupled to a ground level;

Step 115: Dynamically connect and disconnect the floating node and theat least one capacitor to make the at least one capacitor be dynamicallycharged and discharged in response to one exposure time period toreceive energy of the image electric charge;

Step 120: Count the number of times of charging and discharging of theat least one capacitor;

Step 125: Measure a final potential value of the at least one capacitor;

Step 130: Estimate the energy of the image electric charge used todetermine a highest exposure range (or image brightness dynamic range)of the photosensitive pixel according to the number of times of chargingand discharging and the finally measured potential value of the at leastone capacitor; andStep 135: End.

A first embodiment of the present invention is to estimate energy ofimage electric charge by utilizing the charging and discharging behaviorof a single capacitor. Please refer to FIG. 2, which is a diagramillustrating an image sensing circuit 200 according to the firstembodiment of the present invention. The image sensing circuit 200 iscapable of estimating energy of image electric charge of aphotosensitive pixel (which is located outside the image sensing circuit200 and not shown in FIG. 2). The photosensitive pixel means a pixelunit of a photosensitive element. The pixel unit may generate differentamounts of energy of image electric in different light sourceenvironments (different exposure environments). The image sensingcircuit 200 of the present invention is capable of precisely estimatingan amount of energy of image electric charge generated by thephotosensitive pixel and correctly calculating an image brightnessdynamic range. The image sensing circuit 200 of the present invention issuitable for different exposure environments. In the first embodiment, apotential difference increment (or voltage increment) which iscorrespondingly generated by energy of image charge on a singlecapacitor is estimated/determined through the charging and dischargingbehavior of the single capacitor, thereby judging an amount of theenergy of image electric charge equivalently. The image sensing circuit200 includes a floating node FD, a switch circuit 205, a capacitor C1, acounting circuit 210, and an estimation circuit 215. The floating nodeFD is connected to an external photosensitive pixel to receive energy ofimage electric charge generated by the external photosensitive pixel.When the floating node FD receives energy of image electric charge, aconnection between the floating node FD and the estimation circuit 215is cut off. When the floating node FD finishes receiving energy of imageelectric charge, a connection between the floating node FD and theestimation circuit 215 is established, such that the estimation circuit215 can measure a final potential value of the capacitor C1 via thefloating node FD and the switch circuit 205. The switch circuit 205 iscoupled between the floating node FD and the capacitor C1, and isarranged to dynamically connect and disconnect the floating node FD andthe capacitor C1. The capacitor C1 includes a first terminal coupled tothe switch circuit 205, and a second terminal coupled to the groundlevel GND. The counting circuit 210 is coupled to the switch circuit 205and the estimation circuit 215, and is arranged to count a number oftimes of charging and discharging the capacitor C1 according to dynamicswitching of the switch circuit 205, wherein the switch circuit 205performs dynamic switching to make the capacitor C1 be dynamicallycharged and discharged in response to one exposure time period toreceive energy of image electric charge, and the energy of imageelectric charge is determined by the number of times of charging anddischarging (which is counted by the counting circuit 210) and a finallymeasured potential value of the capacitor C1. The estimation circuit 215is coupled to the capacitor C1 and the counting circuit 210, and isarranged to measure a final potential of the capacitor C1. Theestimation circuit 215 estimates the energy of image electric chargeaccording to the number of times of charging and discharging thecapacitor C1 and the finally measured potential value of the capacitorC1, so as to determine a highest exposure range (or image brightnessdynamic range) of the photosensitive pixel.

When the capacitor C1 is ready to be charged (e.g., the potential of thecapacitor C1 is zero) at this moment, the counting circuit 210 controlsthe switch circuit 205 to connect the floating node FD and the capacitorC1, such that the capacitor C1 starts to receive input energy of imageelectric charge. If the capacitor C1 cannot be fully charged with theenergy of image electric charge during a single charging operation,then, under the condition that the potential of the capacitor C1 doesnot exceed a predetermined potential (e.g., a rated highestpotential/voltage), the potential of the capacitor C1 will be finallyraised up to a final potential value VC1 due to the charging behavior.Under this circumstance, the capacitor C1 does not experience a completecharging and discharging behavior once during the process that startsfrom initially receiving energy of the image electric charge and ends atcompletely receiving the energy of image electric charge. Since thecounting circuit 210 is arranged to count a number of times of chargingand discharging the capacitor C1, the number of times of charging anddischarging the capacitor C1 is zero accordingly. Therefore, accordingto the final potential value VC1 of the capacitor C1 and the number oftimes of charging and discharging (which is equal to zero at thismoment), the estimation circuit 215 can determine that the potential ofthe capacitor C1 with a capacitance value is increased by a potentialvalue increment VC1 when the capacitor C1 with the capacitance value isused to receive energy of image electric charge. According to thecapacitance value of the capacitor C1 and the judged potential valueincrement VC1, the amount of energy of image electric charge can beequivalently estimated. According to the judged potential valueincrement VC1, it is capable of calculating the highest exposurestrength (i.e., dynamic range of image) under the current light sourceenvironment.

In addition, the counting circuit 210 detects the capacitor C1 todetermine whether the current potential of capacitor C1 has been chargedto the predetermined potential and to determine whether the currentpotential of capacitor C1 has been discharged to a zero potential. Forexample, the counting circuit 210 can measure the current potential ofthe capacitor C1 to determine whether the current potential of thecapacitor C1 has been charged to the rated highest potential/voltage(i.e., determine whether the capacitor C1 has been fully charged) anddetermine whether the current potential of the capacitor C1 is at a zeropotential due to discharging (i.e., determine whether electric charge isfully discharged). Assume that the rated highest potential/voltage isdesigned to act as the predetermined potential. Considering a case wherethe energy of image electric charge is greater than the energy that canbe stored by the capacitor C1 during a single charging operation, whenthe capacitor C1 has been fully charged with a portion of the energy ofimage electric charge, the counting circuit 210 controls the switchcircuit 205 to perform switching, such that the switch circuit 205 cutsoff a connection between the floating node FD and the capacitor C1, thusmaking the capacitor C1 be discharged. After all electric charge on thecapacitor C1 has been discharged (i.e., after the capacitor C1 is fullydischarged), the counting circuit 210 controls the switch circuit 210 toperform switching again to connect the floating node FD and thecapacitor C1 to continue receiving another portion of the energy ofimage electric charge. At this moment, the counting circuit 210 sets thenumber of charging and discharging the capacitor C1 by one. That is, thebehavior of charging a capacitor from a zero potential to thepredetermined potential (e.g., the rated highest potential/voltage) andsubsequently discharging the same capacitor from the predeterminedpotential to the zero potential is regarded as one complete charging anddischarging behavior. Through repeatedly controlling the dynamicswitching of the switch circuit 205 as mentioned above anddetecting/controlling the charging and discharging behavior of thecapacitor C1 that starts from initially receiving the energy of imageelectric charge and ends at completely receiving the energy of imageelectric charge, the counting circuit 210 can accumulate the number N oftimes of charging and discharging the capacitor C1, where N is apositive integer. The estimation circuit 215 can measure the finalpotential value VC1 of the capacitor C1, and can obtain the number N oftimes of charging and discharging from the counting circuit 210.Therefore, according to the number N of times of charging anddischarging of the capacitor C1 and the final potential value VC1 of thecapacitor C1, the estimation circuit 215 can determine that thepotential of the capacitor C1 with a capacitance value is increased by apotential value increment VC1+VMAX*N when the capacitor C1 with thecapacitance value is used to receive energy of image electric charge,wherein VMAX is the rated highest potential of the capacitor C1 (i.e.,the highest potential value of the capacitor C1 when the capacitor C1 isfully charged). According to the capacitance value of the capacitor C1and the judged potential value increment VC1+VMAX*N, the amount of theenergy of image electric charge can be estimated equivalently. Inaddition, according to the judged potential value increment VC1+VMAX*N,the highest exposure strength (image brightness dynamic range) of thecurrent light source environment can be estimated.

Furthermore, in an alternative design of the first embodiment, theestimation circuit 215 is implemented outside the image sensing circuit200 and thus excluded from the image sensing circuit 200. In otherwords, the image sensing circuit 200 is arranged to control and count anumber of times of charging and discharging the capacitor C1, and thesubsequent estimation operation is performed by an external estimationcircuit. In addition, the switch circuit 205 and the counting circuit210 may be integrated into a same circuit.

A second embodiment of the present invention is to utilize twocapacitors which are sequentially charged and discharged toreplace/simulate a single capacitor, and estimate/determine a potentialdifference increment (or voltage increment) correspondingly generated bythe energy of image electric charge through monitoring the charging anddischarging behavior of the two capacitors, so as to equivalently judgethe amount of the energy of image electric charge. An advantage of sucha design is that a two-capacitor configuration may be implemented byusing capacitors with smaller capacitance to decrease the circuit cost.Please refer to FIG. 3, which is a diagram illustrating an image sensingcircuit 300 according to the second embodiment of the present invention.The image sensing circuit 300 is capable of estimating energy of imageelectric charge of a photosensitive pixel (which is located outside theimage sensing circuit 300 and not shown in FIG. 3). The photosensitivepixel means a pixel unit of a photosensitive element. The pixel unit maygenerate different amounts of energy of image electric charge indifferent light source environments (different exposure environments).The image sensing circuit 300 of the present invention is capable ofprecisely estimating an amount of energy of image electric chargegenerated by a photosensitive pixel and correctly calculating an imagebrightness dynamic range. The image sensing circuit 300 of the presentinvention is suitable for different exposure environments. In the secondembodiment, the potential difference increment (or voltage increment)which is correspondingly generated by energy of image charge oncapacitors is estimated/determined through the charging and dischargingbehavior of the two capacitors C1 and C2, thereby determining an amountof the energy of image electric charge equivalently. The image sensingcircuit 300 includes a floating node FD, a switch circuit 305,capacitors C1 and C2, a counting circuit 310, and an estimation circuit315. The floating node FD is connected to an external photosensitivepixel to receive energy of image electric charge generated by theexternal photosensitive pixel. When the floating node FD receives energyof image electric charge, a connection between the floating node FD andthe estimation circuit 315 is cut off. When the floating node FDfinishes receiving the energy of image electric charge, a connectionbetween the floating node FD and the estimation circuit 315 isestablished, such that the estimation circuit 315 can measure the finalpotential value of the capacitor C1 or C2 via the floating node FD andthe switch circuit 305. The switch circuit 305 is coupled between thefloating node FD and the capacitors C1 and C2, and is arranged todynamically connect and disconnect the floating node FD and thecapacitors C1 and C2. Both of the capacitors C1 and C2 include a firstterminal coupled to the switch circuit 305 and a second terminal coupledto the ground level GND. The switch circuit 305 is connected to one ofthe capacitors C1 and C2, and switches the connection of the other ofthe capacitors C1 and C2. The counting circuit 310 is coupled to theswitch circuit 305 and the estimation circuit 315, and is arranged tocount a number of times of charging and discharging the capacitors C1and C2 according to dynamic switching of the switch circuit 305, whereinthe switch circuit 305 dynamically switches to make the capacitors C1and C2 be dynamically charged and discharged in response to one exposuretime period to receive energy of image electric charge, and the energyof image electric charge is determined by the number of times ofcharging and discharging (which is counted by the counting circuit 310)and a finally measured potential value of the capacitor C1 or C2. Theestimation circuit 315 is coupled to the capacitors C1 and C2 and thecounting circuit 310, and is arranged to measure a final potential ofthe capacitor C1 or C2. The estimation circuit 315 estimates the energyof image electric charge according to the number of times of chargingand discharging the capacitors C1 and C2 and the finally measuredpotential value of the capacitor C1 or C2, so as to determine a highestexposure range (or image brightness dynamic range) of the photosensitivepixel.

When the capacitors C1 and C2 are ready to be charged (e.g., thepotentials of the capacitors C1 and C2 are zero at this moment), theimage sensing circuit 300 receives energy of image electric charge byusing the capacitor C1 first. When the capacitor C1 is fully charged(the rated highest potential/voltage is designed as the predeterminedpotential), the capacitor C2 is used to continuously receive the energyof image electric charge (at this moment, the capacitor C1 is beingdischarged). Alternatively, the image sensing circuit 300 may receiveenergy of image electric charge by using the capacitor C2 first. Whenthe capacitor C2 is fully charged, the capacitor C1 is used tocontinuously receive the energy of image electric charge (at thismoment, the capacitor C2 is being discharged). This is not meant to be alimitation to the present invention. As for the case of charging thecapacitor C1 first, in practice, the counting circuit 310 controls theswitch circuit 305, and connects the floating node FD and the capacitorC1, such that the capacitor C1 starts to receive input energy of imageelectric charge, and a connection between the capacitor C2 and thefloating node FD is cut off. If the capacitor C1 cannot be fully chargedwith the energy of image electric charge during a single chargingoperation, then, under the condition that a potential of the capacitorC1 does not exceed the rated highest potential of the capacitor C1, thepotential of the capacitor C1 will be finally raised up to a finalpotential value VC1 due to the charging behavior. Under thiscircumstance, in the process that starts from initially receiving energyof the image electric charge and ends at completely receiving the energyof image electric charge, the capacitor C1, C2 does not experience acomplete charging and discharging behavior once. Since the countingcircuit 310 is arranged to count a number of times of charging anddischarging the capacitor C1, C2, the number of times of charging anddischarging the capacitor C1, C2 is zero accordingly. Therefore,according to the number of charging and discharging (which is equal tozero at this moment) and the final potential value of the capacitor C1(at this moment, the potential of the capacitor C2 is zero), theestimation circuit 315 can determine that the potential of the capacitorC1 with a capacitance value is increased by a potential value incrementVC1 when the capacitor C1 with the capacitance value is used to receiveenergy of image electric charge. According to the capacitance of thecapacitor C1 and the judged potential value increment VC1, the amount ofenergy of image electric charge can be equivalently estimated. Accordingto the judged potential value increment VC1, it is capable ofcalculating the highest exposure strength (i.e., dynamic range of image)of current light source environment.

In addition, the counting circuit 310 detects the capacitor C1, C2 todetermine whether the capacitor C1, C2 has been fully charged anddetermine whether the capacitor C1, C2 has been discharged to zeropotential. Assume that the energy of image electric charge is greaterthan the energy that could be stored in the capacitor C1 or C2 during asingle charging operation. As far as charging the capacitor C1 first isconcerned, when the capacitor C1 is fully charged with a portion of theenergy of image electric charge, the counting circuit 310 controls theswitch circuit 305 to perform switching, such that the switch circuit305 cuts off a connection between the floating node FD and the capacitorC1 so as to make the capacitor C1 be discharged, and the switch circuit305 establishes a connection between the floating node FD and thecapacitor C2 so as to make the capacitor C2 start to receive anotherportion of the energy of image electric charge to perform charging. Whenthe capacitor C2 is fully charged (it should be noted that the potentialof the capacitor C1 is discharged to the zero potential before thecapacitor C2 is fully charged), the counting circuit 310 controls theswitch circuit 305 again to perform switching, such that the switchcircuit 305 cuts off the connection between the floating node FD and thecapacitor C2 so as to make the capacitor C2 be discharged, and theswitch circuit 305 establishes a connection between the floating node FDand the capacitor C1 so as to make the capacitor C1 start to receive aportion of the energy of image electric charge again to performcharging. At this moment, the counting circuit 310 sets the number oftimes of charging and discharging the capacitor C1 and the number oftimes of charging and discharging the capacitor C2 by one, respectively.Through repeatedly controlling the dynamic switching of the switchcircuit 305 as mentioned above and detecting/controlling the chargingand discharging behavior of the capacitors C1 and C2 that starts frominitially receiving the energy of image electric charge and ends atcompletely receiving the energy of image electric charge via thecapacitors C1 and C2, the counting circuit 310 can accumulate the numberN1 of times of charging and discharging the capacitor C1 (N1 is apositive integer), and accumulate the number N2 of times of charging anddischarging the capacitor C2 (N2 is a positive integer). N1 is equal toN2. The estimation circuit 315 can measure the final potential value VC1(or VC2) of the capacitor C1 (or C2), and can obtain the numbers N1, N2of charging and discharging from the counting circuit 310. Therefore,according to the numbers N1, N2 of times of charging and discharging andthe final potential value VC1 (or VC2) of the capacitor C1 (or C2), theestimation circuit 315 can determine that the potential of capacitorsthat are connected in parallel and have a total capacitance value isincreased by a potential value increment VC1+VMAX1*N1+VMAX2*N2 or apotential value increment VC2+VMAX1*N1+VMAX2*N2 (depending on whetherthe finally measured potential value is the final potential value VC1 ofthe capacitor C1 or the final potential value VC2 of the capacitor C2)when a designed capacitor combination of capacitors C1 and C2 withrespective capacitance values is used to receive energy of imageelectric charge, wherein VMAX1 and VMAX2 are the rated highestpotentials of the capacitors C1 and C2 (i.e., the highest potentialvalues of the capacitors C1 and C2 when the capacitors C1 and C2 arefully charged), respectively. According to the capacitance values of thecapacitors C1 and C2 and the judged potential value incrementVC1+VMAX1*N1+VMAX2*N2 or VC2+VMAX1*N1+VMAX2*N2, the amount of the energyof image electric charge can be equivalently estimated. According to thejudged potential value increment as mentioned above, it is capable ofestimating the highest exposure strength (dynamic range of image) of thecurrent light source environment.

Furthermore, in an alternative design of the second embodiment, theestimation circuit 315 may be implemented outside the image sensingcircuit 300 and thus excluded from the image sensing circuit 300. Inother words, the image sensing circuit 300 is arranged to control andcount a number of times of charging and discharging the capacitor C1 anda number of times of charging and discharging the capacitor C2, and thesubsequent estimation operation is performed by an external estimationcircuit. In addition, the switch circuit 305 and the counting circuit310 may be integrated into a same circuit. Moreover, the capacitors C1and C2 may be implemented with capacitors having the same capacitancevalue or capacitors having different capacitance values. If thecapacitors C1 and C2 are implemented with capacitors having differentcapacitance values, the estimation circuit 315 must refer to thedifferent capacitance values of the capacitors C1 and C2, the judgedrespective potential value increments VMAX1*N1 and VMAX2*N2, and thefinal potential value (VC1 or VC2) to estimate the amount of the energyof image electric charge and determine the highest exposure strength(dynamic range of image) of the current light source environment. On thecontrary, if the capacitors C1 and C2 are implemented with capacitorshaving the same capacitance value, potential value incrementscorresponding to different capacitors C1 and C2 can be accumulated, andthe calculation performed by the estimation circuit 315 is simpler andeasier to be carried out.

Moreover, the operation of sequentially charging and discharging twocapacitors in the present invention may be implemented with an automatedcontrol mechanism. Please refer to FIG. 4, which is a diagramillustrating an image sensing circuit 400 according to a thirdembodiment of the present invention. The image sensing circuit 400 iscapable of estimating energy of image electric charge of aphotosensitive pixel (which is located outside the image sensing circuit400 and not shown in FIG. 4). The photosensitive pixel means a pixelunit of a photosensitive element. The pixel unit may generate differentamounts of energy of image electric charge in different light sourceenvironments (different exposure environments). The image sensingcircuit 400 of the present invention can precisely estimate an amount ofenergy of image electric charge generated by the photosensitive pixel,and correctly calculate an image brightness dynamic range. The imagesensing circuit 400 of the present invention is suitable for differentexposure environments, and determines energy of image electric chargethrough the charging and discharging behavior of two capacitors C1 andC2. The image sensing circuit 400 includes a floating node FD, a switchcircuit 405, capacitors C1 and C2, a counting circuit 410, and anestimation circuit 415. The switch circuit 405 includes four switchesM1, M2, M3, and M4 and a switch controller (which includes invertersINV1 and INV2). The switches M1-M4 are implemented with fourtransistors. The switch M1 is connected between the floating node andthe capacitor C1. The switch M2 is connected between the floating nodeFD and the capacitor C2. The switch M3 is connected between thecapacitor C1 and the ground level GND. The switch M4 is connectedbetween the capacitor C2 and the ground level GND. The states of theswitches M1 and M4 are controlled by signal Q, and the states of theswitches M2 and M3 are controlled by signal QB, wherein the signals Qand QB are generated by the switch controller that is composed ofinverters INV1 and INV2 to automatically control the switch circuit 405to automatically perform dynamic switching. The signals Q and QB are outof phase. According to the structure of the circuit, the inverter INV1includes an input terminal and an output terminal. The input terminal ofthe inverter INV1 is coupled to the potential level (FD1) of thecapacitor C1, and the signal Q at the output terminal of the inverterINV1 is arranged to control the states (e.g., an open-circuit state oran closed-circuit state) of the switches M1 and M4. The inverter INV2includes an input terminal and an output terminal. The input terminal ofthe inverter INV2 is coupled to the potential level (FD2) of thecapacitor C2, and the signal QB at the output terminal of the inverterINV2 is arranged to control the states (e.g., an open-circuit state or aclosed-circuit state) of the switches M2 and M3. The input terminal ofthe inverter INV1 is coupled to the output terminal of the inverterINV2, and the input terminal of the inverter INV2 is coupled to theoutput terminal of the inverter INV1. When the switches M1 and M4 arecontrolled by the signal Q to be switched on, the signal QB controls theswitches M2 and M3 to be open-circuited to cut off the connection.Hence, the potential FD1 of the capacitor C1 is coupled to the floatingnode FD without being coupled to the ground level GND, and the capacitorC1 is arranged to perform charging to receive energy of image electriccharge. In addition, the potential FD2 of the capacitor C2 is connectedto the ground level GND to perform discharging. On the contrary, whenthe switches M2 and M3 are controlled by the signal QB to be switchedon, the signal Q controls the switches M1 and M4 to be open-circuited tocut off the connection. Hence, the potential FD1 of the capacitor C1 iscoupled to the ground level GND to perform discharging. The potentialFD2 of the capacitor C2 is coupled to the floating node FD without beingcoupled to the ground level GND, and the capacitor C2 is arranged toperform charging to receive energy of image electric charge. Theabove-mentioned automated control mechanism is that, in the process ofcharging the potential FD1 of the capacitor C1 from the zero potentialto the rated highest potential, the operation of the inverters INV1 andINV2 enables the signal Q to switch from a high potential to a lowpotential, and enables the signal QB to switch from a zero potential toa high potential. In this way, the switch M1 is controlled to switchfrom a closed-circuit state to an open-circuit state, and the switch M3is controlled to switch from an open-circuit state to a closed-circuitstate, such that the capacitor C1 automatically starts to performdischarging as soon as the capacitor C1 is charged to the rated highestpotential. Similarly, the capacitor C2 is controlled to automaticallystart to perform discharging as soon as the capacitor C2 is charged tothe rated highest potential.

In addition to the operation of counting the number of times of chargingand discharging a capacitor or judging the charging and dischargingbehavior of a capacitor via detecting a potential change of a terminalof the capacitor as described in the above-mentioned first and secondembodiments, the counting circuit 410 can count a number of signal leveltransitions of the signals Q and QB to count a number of times ofcharging and discharging the capacitors C1 and C2. Please refer to FIG.5, which is a diagram illustrating the signal waveforms of the signals Qand QB shown in FIG. 4. As shown in FIG. 5, T1 through T7 correspond tothe signal pulses of the signals Q and QB, and represent the chargingorders of the capacitors C1 and C2. For example, the capacitor C1 isfirst charged at T1, the capacitor C2 is charged and the capacitor C1 isdischarged at T2, and so on. At T7, the capacitor C1 is charged tocompletely receive the remaining energy of image electric charge. Inpractice, the counting circuit 410 can count the signal transitions ofrising edges and falling edges of the signals Q and QB to determinewhether the capacitors C1 and C2 have accomplished a complete chargingand discharging behavior once. For example, the counting circuit 410detects a rising edge and a falling edge of a signal pulse (whichcorresponds to T1) of the signal Q to judge that the capacitor C1currently finishes a complete charging and discharging behavior once,and thus sets the number of times of charging and discharging thecapacitor C1 by one. In this way, the counting circuit 410 of thisexample therefore can count that each of the capacitors C1 and C2finally have the complete charging and discharging behavior three times.In addition, the operation and function of the estimation circuit 415are similar to that of the estimation circuit 315 shown in FIG. 3, andthe detailed description thereof is omitted here for brevity.

Moreover, the present invention can estimate an amount of energy ofimage electric charge by counting the charging and discharging behaviorof three or more capacitors, wherein the design of a switch circuit mayinclude multiple switches corresponding to the number of three or morecapacitors, and the switch circuit is arranged to switch on at least oneswitch at any time such that at least one corresponding capacitor can beused for charging to receive energy of image electric charge, and atleast one switch is in an open-circuit state such that there is at leastanother capacitor used for discharging. For example, when the chargingand discharging behavior of three capacitors is utilized to estimate anamount of energy of image electric charge, the switch circuit can bedesigned to have the first switch that is switched on (i.e., in aclosed-circuit state), the second switch that is in an open-circuitstate, and the third switch that may be about to be switched from anopen-circuit state to a closed-circuit state or may just enter theclosed-circuit state, such that there is at least one capacitor that canbe used for charging, and there is one capacitor which is performingdischarging. For example, after the first capacitor that corresponds tothe first switch and is originally used for charging has been chargedfor a period of time and is about to perform discharging, the thirdswitch has been switched from an open-circuit state to a closed-circuitstate, such that the third capacitor has started to perform charging. Anadvantage of such design is that energy of image electric charge can beseamlessly and sequentially received by the three capacitors.

It should be noted that, in the above-mentioned embodiments, thepotential of a capacitor is discharged to a zero potential when thecapacitor performs discharging. However, this is not meant to be alimitation to the present invention. In other alternative designs, thepotential of a capacitor may be discharged to a lower potential when thecapacitor performs discharging, and the above-mentioned estimationcircuit only needs a slight modification on the estimation of apotential value increment generated by energy of image electric charge.For example, the calculation approach for a potential value incrementgenerated due to a single charging operation is just changed from anincrement calculation method that calculates an increment from a zeropotential to a predetermined potential to another increment calculationmethod that calculates an increment from a lower voltage potential to apredetermined potential.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. An image sensing circuit comprising: a floatingnode, arranged to receive image electric charge from a photosensitivepixel; a switch circuit, coupled between the floating node and at leastone capacitor, the switch circuit arranged to dynamically connect anddisconnect the floating node and the at least one capacitor; the atleast one capacitor, comprising a first terminal coupled to the switchcircuit and a second terminal coupled to a ground level; and a countingcircuit, coupled to the switch circuit, the counting circuit arranged tocount a number of times of charging and discharging the at least onecapacitor according to dynamic switching of the switch circuit; whereinthe switch circuit dynamically switches to make the at least onecapacitor be dynamically charged and discharged in response to oneexposure time period to receive energy of the image electric charge, andthe energy of the image electric charge is determined by the number oftimes of charging and discharging counted by the counting circuit and afinally measured potential value of the at least one capacitor.
 2. Theimage sensing circuit of claim 1, wherein the counting circuit isfurther arranged to: control the switch circuit to connect the floatingnode and the at least one capacitor to receive a portion of the energyof the image electric charge; control the switch circuit to cut off aconnection between the floating node and the at least one capacitor tomake the at least one capacitor be discharged when the at least onecapacitor is fully charged with the portion of the energy of the imageelectric charge; and control the switch circuit to connect the floatingnode and the at least one capacitor again to receive another portion ofthe energy of the image electric charge after the at least one capacitorfinishes discharging.
 3. The image sensing circuit of claim 1, furthercomprising: an estimation circuit, coupled to the at least one capacitorand the counting circuit, the estimation circuit arranged to measure afinal potential of the at least one capacitor, and estimate the energyof the image electric charge according to the number of times ofcharging and discharging of the at least one capacitor and the finallymeasured potential value of the at least the capacitor, wherein theenergy of the image electric charge used is used to determine a highestexposure range of the photosensitive pixel.
 4. The image sensing circuitof claim 1, wherein the at least one capacitor comprises a firstcapacitor and a second capacitor, and the switch circuit comprises: afirst switch, connected between the floating node and the firstcapacitor; a second switch, connected between the floating node and thesecond capacitor; a third switch, connected between the first capacitorand the ground level; and a fourth switch, connected between the secondcapacitor and the ground level; wherein when the first switch and thefourth switch are switched on, the first capacitor is arranged toperform charging to receive the energy of the image electric charge, andthe second capacitor is arranged to perform discharging; and when thesecond switch and the third switch are switched on, the second capacitoris arranged to perform charging to receive the energy of the imageelectric charge, and the first capacitor is arranged to performdischarging.
 5. The image sensing circuit of claim 4, wherein the switchcircuit further comprises a switch controller, and the switch controllercomprises: a first inverter, comprising an input terminal and an outputterminal, wherein the input terminal of the first inverter is coupled toa potential level of the first capacitor, a first signal at the outputterminal of the first inverter is arranged to control states of thefirst switch and the fourth switch; and a second inverter, comprising aninput terminal and an output terminal, the input terminal of the secondinverter is coupled to a potential level of the second capacitor, asecond signal at the output terminal of the second inverter is arrangedto control states of the second switch and the third switch; wherein theinput terminal of the first inverter is coupled to the output terminalof the second inverter, and the input terminal of the second inverter iscoupled to the output terminal of the first inverter.
 6. The imagesensing circuit of claim 5, wherein the first signal is an invertingsignal of the second signal, and the counting circuit counts a number ofsignal level transitions of the first signal and the second signal tocount a number of times of charging and discharging the first capacitorand a number of times of charging and discharging the second capacitor.7. The image sensing circuit of claim 1, wherein the at least onecapacitor comprises three capacitors, and the switch circuit switches onat least one switch at any time to make at least a capacitor in thethree capacitors be used for charging to receive the energy of the imageelectric charge.
 8. A method applied to an image sensing circuit,comprising: providing a floating node arranged to receive image electriccharge from a photosensitive pixel; utilizing a switch circuit coupledbetween the floating node and at least one capacitor, wherein the atleast one capacitor comprises a first terminal coupled to the switchcircuit and a second terminal coupled to a ground level; dynamicallyconnecting and disconnecting the floating node and the at least onecapacitor to make the at least one capacitor be dynamically charged anddischarged in response to one exposure time period to receive energy ofthe image electric charge; and counting a number of times of chargingand discharging the at least one capacitor; wherein the energy of theimage electric charge is determined by the counted number of times ofcharging and discharging of the at least one capacitor and a finallymeasured potential value of the at least one capacitor.
 9. The method ofclaim 8, wherein the step of dynamically connecting and disconnectingthe floating node and the at least one capacitor to make the at leastone capacitor be dynamically charged and discharged in response to oneexposure time period to receive the energy of the image electric chargecomprises: connecting the floating node and the at least one capacitorto receive a portion of the energy of the image electric charge; cuttingoff a connection between the floating node and the at least onecapacitor to make the at least one capacitor be discharged when the atleast one capacitor is fully charged with the portion of the energy; andconnecting the floating node and the at least one capacitor again toreceive another portion of the energy of the image electric charge whenthe at least one capacitor finishes discharging.
 10. The method of claim8, further comprising: measuring a final potential of the at least onecapacitor; and estimating the energy of the image electric chargeaccording to the number of times of charging and discharging of the atleast one capacitor and the finally measured potential value of the atleast one capacitor, wherein the energy of the image electric charge issued to determine a highest exposure range of the photosensitive pixel.11. The method of claim 8, wherein the at least one capacitor comprisesa first capacitor and a second capacitor, and the step of dynamicallyconnecting and disconnecting the floating node and the at least onecapacitor to make the at least one capacitor be dynamically charged anddischarged in response to one exposure time period to receive the energyof the image electric charge comprises: utilizing the first capacitorwhich performs charging to receive the energy of the image electriccharge, and discharging the second capacitor; and utilizing the secondcapacitor which performs charging to receive the energy of the imageelectric charge, and discharging the first capacitor.
 12. The method ofclaim 8, wherein the at least one capacitor comprises three capacitors,and the step of dynamically connecting and disconnecting the floatingnode and the at least one capacitor to make the at least one capacitorbe dynamically charged and discharged in response to one exposure timeperiod to receive the energy of the image electric charge comprises:switching on at least one switch at any time to make at least acapacitor in the three capacitors be used for charging to receive theenergy of the image electric charge.